Laser-based high heat flux testing for power exhaust in fusion devices

One of the critical challenges in realizing fusion energy is the survival and cooling of the Plasma Facing Components (PFCs) in the extreme environment (>1000°C and constant neutron bombardment). In the DEMOnstration Power Plant (DEMO), the divertor must endure steady state loads of 10MWm2and transient thermal cycling up to 20MWm2. Novel target designs are needed to cope with this thermal load. An optics system was designed to replicate the thermal environment in DEMO. A new facility, coined the Oxford Laser Heating Facility (OLAHF), has been established for laser-based heating tests. A Compound Parabolic Concentrator (CPC) was designed to focus the power from four laser modules to greater than 5MWm2 onto a target that absorbs 98.9% of the incident light. Numerical, thermomechanical studies on the steady-state performance confirmed that the deformation of the CPC does not exceed 0.4 mm and that the maximum temperature of the glass is less than 30°C. A novel divertor target, termed the Spiral Plate Module (SPM), was designed to meet the fusion-relevant requirements. The geometry of the SPM was initially optimized by a one-dimensional model, the results of which showed a good correlation to Computational Fluid Dynamics (CFD) studies. The SPM achieved the lowest walloverheat (τs) and dimensionless mass flow rate (m∗) of any target design considered, and showed good hydraulic performance such that the power needed to pump the coolant is only 0.32% of the incident heat flux. Lastly, a method was created to control the lasers and monitor the processes within OLAHF. Through a number of Labview panels, the operator can vary the laser power in time and record and store experimental data, and the program will send a warning or shut down all systems (depending on severity) if there is a possibility of harm to the hardware or users.